This application claims the benefit of and priority from Japanese Applications No. 2000-92903 filed Mar. 30, 2000 and No. 2000-396453 filed Dec. 27, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel cutoff valve to be mounted on an upper wall of an automobile fuel tank. The fuel cutoff valve permits an outflow of fuel vapors in the tank during refueling and, restricts the fuel outflow when the fuel reaches a predetermined level.
2. Description of Related Art
FIG. 10 shows a structure of a prior art cutoff valve. A fuel cutoff valve 100 is mounted on an upper tank wall FTa of a fuel tank FT, and comprises a casing 102, a cover 110, a float 120, and a spring 130. The casing 102 comprises a top wall 103, a side wall 104 of unitary construction having an outside edge formed of top wall 103, and a base plate 105 attached to a bottom end of the side wall 104 so as to define an internal space forming a valve chest 102S.
Within the valve chest 102S is housed the float 120 having a valve portion 120a in its upper portion. This valve portion 120a opens and closes a connecting passage 103d connecting to the outside of the fuel tank FT. The float 120 is supported by the spring 130 arranged on the base plate 105.
The cover 110 comprises a cover main body 112 for attaching to the casing 102, a cover passage forming portion 114, and a flange 115, these elements being of unitary construction. The cover main body 112 has a mounting recess 114a formed therein, and fitting into an upper welding portion 103b of the top wall 103 of the casing 102. An engaging protuberance 103a is formed at the top of the casing 102, wherein the casing 102 and the cover 110 are assembled together by engagement with an engagement hole 112a of a support member of the cover 110. The flange 115 is thermally welded to the upper tank wall FTa of the fuel tank FT via a joining end face 115a. 
To mount the fuel cutoff valve 100 on the upper tank wall FTa of the fuel tank FT, the float 120 and the spring 130 are installed within the casing 102, which is then attached with the base plate 105. The casing 102 is then installed in the cover 110. Specifically, after installing an O-ring 140 in an annular recession (not shown) in the upper projecting portion 103b of the casing 102, the upper projecting portion 103b is fitted into the mounting recess 114a of the cover 110. The joining end face 115a of the flange 115 is heated with a thermal fusing plate (not shown), and the rim area of a tank fixation hole FTc of the fuel tank FT is also heated with a thermal fusing plate (not shown). The melted portions are then thermally welded together.
In the conventional art, the cover 110 and the upper tank wall Fta are both made of a polyethylene material in order to permit fusing of the cover 110 to the upper tank wall FTa. Thus, fuel vapor present within the fuel tank FT can permeate through the cover 110, albeit in small quantities, and emitted into the atmosphere. From an environmental standpoint, it is desirable to reduce such fuel vapor emissions as much as possible.
The present invention provides a fuel cutoff valve that reduces the release of fuel vapors from fuel tanks into the atmosphere.
To solve this problem, an exemplary first embodiment of the present invention provides a fuel cutoff valve that is to be partly inserted in a fixation hole formed in an upper tank wall of a fuel tank, the upper tank wall being made of a first resin material. The fuel cutoff valve comprises a cover that includes a circular welding end constructed and arranged to be thermally welded to the upper tank wall to surround a circumference of the fixation hole, and a fuel conduit that is constructed and arranged to connect to outside. The fuel cutoff valve also comprises a casing that is made of a second resin material which has a greater fuel permeation-resistant property than the first resin material, the casing including a valve chest that is constructed and arranged to connect the fuel tank to the fuel conduit. A valve body is positioned in the valve chest to open and close the fuel conduit according to a level of a liquid fuel in the fuel tank. The cover is made of a third resin material containing the first and second resin material such that the first material is dispersed in a matrix of the second resin material.
The fuel cutoff valve is mounted on the top wall of the fuel tank. When the level of fuel rises as the tank is refueled, fuel vapor present within the fuel tank flows to the outside (a canister) through a connecting passage. When the fuel in the fuel tank reaches a predetermined level, the increased buoyant force on the float causes it to rise, blocking the connecting passage and preventing the fuel from flowing out of the fuel tank.
The cover of the fuel cutoff valve is made of a matrix of a second resin having excellent resistance to permeation by fuel, and contains added thereto as a dispersed phase, the same first resin material used for the fuel tank. Since the cover is made of a matrix of the second resin, emission of fuel vapor into the atmosphere through permeation through the cover is prevented. Since the cover also contains the first resin material as a dispersed phase, the cover can be welded to the upper tank wall, which is made of the same resin material as the dispersed phase.
Thus, when the fuel cutoff valve is installed on the upper tank wall, by welding the annular welding portion of the cover to the upper tank wall, the fixation hole is blocked to seal the tank interior from the outside. Therefore, emission of fuel vapor into the atmosphere from the highly fuel permeation-resistant cover can be prevented.
In a preferred embodiment of the invention, the cover and casing are supported via a sealing member, thereby ensuring a good seal between the cover and the casing.
In another preferred embodiment, the casing is unified with the cover by means of welding. This permits dispensing of the seal member, thus reducing the number of parts required.
A second exemplary embodiment of the present invention provides a fuel cutoff valve that is to be partly inserted in a fixation hole formed in an upper tank wall of the fuel tank, the upper tank wall being made of a first resin material. The fuel cutoff valve comprises a casing that includes a tubular side wall to be inserted in the fixation hole, a top wall to be integrally formed with the side wall, and a flange formed along a periphery of the top wall so as to cover an outside periphery of the fixation hole. A fuel conduit is constructed and arranged to connect to an outside portion of the side wall and the top wall defining a valve chest. The fuel cutoff valve also comprises a float that is accommodated in the valve chest to open and close the fuel conduit according to a level of a liquid fuel in the fuel tank. The casing is made of a resin material containing the first resin material and a second resin material which has greater fuel permeation-resistant property than the first resin material. The resin material of the casing is made such that the first resin material is dispersed in a matrix of the second resin material.
The second exemplary embodiment also comprises a casing made of a cover and casing of unitary construction. The casing is made of a resin material having a matrix of the second resin material and containing the first resin material as a dispersed phase, thereby reducing the number of parts required.
In a preferred embodiment of the fuel cutoff valve, the cut off valve comprises a weld fixing member fixed to the cover, the weld fixing member being made of the first resin material and having a weld fixing end welded to the upper tank wall integrally with the annular welding end of the cover. According to this embodiment, in cases where the first resin content of the cover is held to a minimumxe2x80x94which has the effect of reducing bond strength with the upper tank wallxe2x80x94in order to ensure good resistance to fuel permeation, the weld fixing memberxe2x80x94which is made of the same material as the upper tank wallxe2x80x94provides the necessary bond strength to the upper tank wall, allowing the cover to be integrally mounted onto the upper tank wall. Further, it is sufficient for the cover to bond tightly enough to the upper tank wall to control fuel permeation, so mounting strength need not be a consideration in resin material formulation. This simplifies selection of the proportions of the first resin material and second resin material and affords greater latitude as to the proportions thereof.
A third exemplary embodiment of the present invention provides a fuel cutoff valve that is to be partly inserted in a fixation hole formed in an upper tank wall of a fuel tank, the upper tank wall being made of a first resin material. Here, the fuel cutoff valve comprises a cover that includes a circular welding end that is constructed and arranged to be thermally welded to the upper tank wall to surround a circumference of the fixation hole. A fuel conduit is constructed and arranged to connect to an outside location of the fuel cutoff valve. The fuel cutoff valve also comprises a casing that is made of a second resin material, which has greater fuel permeation-resistant property than the first resin material, the casing including a valve chest that is constructed and arranged to connect the fuel tank to the fuel conduit. Also included is a valve body that is accommodated in the valve chest to open and close the fuel conduit according to a level of a liquid fuel in the fuel tank. A barrier layer is formed on a surface of the cover, the barrier layer being made of a resin material with greater fuel permeation-resistant property than the cover material.
According to the third exemplary embodiment of the present invention, the cover is made of the first resin material to assure weldability thereof to the upper tank wall, and the surface of the cover is provided with a barrier layer with excellent resistance to permeation by fuel, thereby preventing emission of fuel vapors from within the fuel tank into the atmosphere.